Operational and instrumentation amplifiers (OPA2333, OPA333, INA333)

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A friend approached me to check if I could make his circuit work.
Bunch of wires all over the breadboard (sorry no photo) with OPA2333, OPA333, INA333 on it. ūüôā
Most too long to see, some broken off and a short on pin 7 and 8 on INA333.

SLIKA celotnega vezja

Steps to a working circuit?:
– make good solder joints OK
– check continuity between smd IC and breadboard OK
– trim DIY pcb to size OK
– add supply voltage OK

SLIKA fon slika

– check correct operation of OPA2333 & OPA333 in voltage follower conf.
Use supply voltage of 5V and GND. Check transition between voltage divider and button press (GND), which shorts lower resistor

SLIKA if datasheeta za voltage follower
SLIKA verja, fon

OPA2333 4xOK

– check correct operation of INA333
V+ = 5 V
V- = GND
Vin- = 2.77 V
Vin+ = 3.32 V
G=1 (R=NC) Vo=0.56
G=2 (R=100 k) Vo=1.10
G=3 (R= 50 k) Vo=1.68

Vin- = 0.010 V
Vin+ = 0.015 V
G=1 (R=NC) Vo=0.0.005
G=2 (R=100 k) Vo=0.01
G=3 (R= 50 k) Vo=0.015

– Connect RA and LA part of the circuit to Gina=5 with dc and Ref=2.5V (same as for final stage Vin+). Final stage G=200 with OPA2333 (OPA333)
SLIKA, pobarvana z rumeno



– Provida a small difference in voltage (LA-RA RG=25 k
G = 1+(100 k/25 k) = 1+4 = 5
final stage has 1/2 Vs “reference” on Vin+


Implemented this configuration.


– Signal generator in range of 0-200 Hz?
I found an awesome program to output known voltage from audio card dac.


2x SLIKA, ńćeked with osciloscope

-Check if suitable as input to RA and LA

update: fucking music, ruined it all, almost ūüôā (I didn’t know music is running in background)

Hm. Ground, noise, long wires, osciloscope. WIth final stage gain of 200, it goes in saturation almost all time. When 1 Mohm is replaced with 11 kohm, then with a gain of -2 we get

SO final stage works.

SLIKA Gain=-2


SLIKE, ko kao deluje 15.8. 00:16


-Introduce an OPA for LL input and 2x OPAs for RL (Neutral) output

-Wait for other to pads to come to me. Prepare circuit according example and test by placing pads.


Written by luftek

August 12th, 2016 at 6:49 pm

Posted in Make

LimeSDR enclosure, PCB – front and rear panel

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sample_v3_assembly (3) present_kit


I forked LimeSDR repo on Github for the purpose of enclosure: https://github.com/luftek/LimeSDR-USB
Now I sent two PCB panels to owners (I am waiting for mine from Crowdsupply)Probably not good regarding EMI (Electromagnetic Interference) as it is aluminium shell, which is also painted (isolation). But is good as mechanical protection.

I decided for 97x40x100, but enclosures of 76x35x100 are easier to come by and more portable. Maybe also try smaller version.

GitHub: https://github.com/luftek/LimeSDR-USB

update 14.8.:
eBay listing http://www.ebay.com/itm/NO-STOCK-LimeSDR-enclosure-front-rear-panel-case-rtl-sdr-myriad-hackrf-airspy-/112088499793 did well ūüôā Sold off all of remaining panels from 1st batch in 3 days. Now I have the funds to order for 76x35x100 enclosure

Written by luftek

August 10th, 2016 at 3:07 pm

Posted in pcb

Lets have some PCBs made

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me + KiCad + PCB Panelizer Beta + Dirty PCB = great job! for first PCBs after some time


Written by luftek

May 7th, 2016 at 2:59 pm

Posted in Uncategorized

KM switch inside a desktop computer, custom PCB – DRAFT

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KVM switch stands for (Keyboard, Video, Mouse) switch. When wanting to¬†utilize my setup of two 24″ monitors and keyboard + mouse¬†for¬†friends or work laptop I would need to make all connections piece by piece. So VGA, DisplayPort, keyboard and mouse.

Both monitors have 2 connections possible, so using another pair of cables for laptop is convenient. Then just switch video input on monitor.
Transitioning in case of keyboard and mouse is not so.

Currently I have this KVM switch inside my desktop computer. It uses

slike installlacije v rańćunalniku¬†

Kako bi kit izgledal:




PCB internal:
pcb  front_plate (missing some holes)

Enclosure front plate:



solution similar to http://www.ebay.com/itm/LINDY-KM-Tastatur-Maus-Switch-USB-fur-2-Rechner-32165-/301729173160


slike nameńći v mapo, naredi enostavno skico in sklice na dele.


Shematics of KM part:


Dropbox shared folder:
‚Äúproject‚ÄĚ folder


Written by luftek

March 2nd, 2016 at 10:28 pm

Posted in Uncategorized

Voltmeter, Ampermeter, 5 digit 7 segment, my own code

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Few years back I purchased low cost (range of 100‚ā¨) Power Supply HY3005D, rated for 30V and 5A. Just after few weeks I started to dislike the whole situation with LCD display w/o backlight and w/ really bad viewing angles. First option, for the reseller to give¬†parts for an upgrade, didn’t happen. 2nd DIY backlight solved visibility at low light, but viewing angles remained. Not long ago¬†I searched for voltmeters and ampermeters in this kind of form factor, to fit existing front panel.


After some measuring and searching on online marketplaces I came across a suitable option:¬†ebay.com/itm/310672415584¬†(reseller:¬†alice1101983¬†is recommended and reliable source of electronics kits& parts). I purchased 2x in a wish to change 2nd from Volt to Amp meter. Voltmeter works no problem. Vin is divided through a resistor ladder of 330 kő© and 20 kő©. These way input of 0 – 33 V is reduced to¬†20/(330+20) of Vin. ¬†Knowing that voltage on shunt resistor definitely won’t reach limit I removed both resistors and shorted R3. At that time I didn’t look more into it. Comparison of multimeter and ampermeter on left side of Supply.

voltmeter comparison of multimeter and ampermeter values voltemeter backside

So ampermeter kind of works if you know you need to double the shown number. ūüôā Well, not quite. As far I know resistor ladder can only divide not multiply the input voltage. The whole time I had in my mind I can just reprogram the microcontroller similarly (1|2) and correct the scaling.¬†So I ordered 1 more. Also asked the seller (alice) to contact the possible manufacturer¬†world.taobao.com/item/15073358476.htm. I got a negative replay. Today I decided¬†to contact the supplier shop59318659.taobao.com¬†directly, first using TaoBao online page chat and then using their chat app. Thankfully I found ScreenTranslator that made installation¬†little easier. No matter the unusual time (Friday night in China) supplier responded in English. Of coarse they didn’t gave me changed binaries. That would be awesome indeed. They forwarded¬†me to forum post on this voltmeter. There is a 18bit ADC present (MCP3421, SOT23-6) which is quite nice for whole voltmeter price of 4$¬†(ADC cost about 1$/pcs @10pcs order).



Design conciderations:
Why not use I2C (pins 11 and 12) that is present in chip? Original bit-bangs I2C over pins 17 and 18.
Using SWIM pin as GPIO is not great for coding and debugging. Specially when this pin is utilized as part of communication (I2C). Download code -> start Debug -> disable Debug

1of5 digit duration  logic_one_frame_voltmeter_3.6V


Power supply uses 30 mő© shunt resistor. Which results in 150 mV @ 5 A. I removed voltage divider resistors and shorted
ADC range is ¬Ī2.048 V. Using built in PGA 8x (Programable Gain Amplifier) changed¬†max. voltage range presented to ADC input to 1200 mV. Decided for offset of 28 mA.

shunt resistor max. shunt voltage 160 mA 500 mA


Coding the segments and digits was easy. Replicating the I2C with similar timings to original needed more brain stretching. Also took me quite a lot of plugging and unplugging of ST-LINK. Last was to code the appropriate scale and possible offset. I did think about using input pin intended for push button, as a trigger for calibration but went with static definition usable in my case.  Also needed to unplug the programmer and plug in power supply.

Dropbox shared folder:
“project” folder


Written by luftek

February 28th, 2016 at 3:51 am

Posted in Make,pcb,Reuse

No Store page

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That is all there is to it. Adapter and cable are only available on eBay http://www.ebay.com/usr/luftek

Written by luftek

August 3rd, 2015 at 8:06 pm

Posted in Uncategorized

Smart watch from Weloop/GoClever

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Previous watches

I had problems with my Metawatch as did everybody else. Does freaking OLED displays didn’t last long (read comments on prev post). I returned it to TI and they refunded me in full. So I forget about the watches for a while, I wear a standard one (Casio) for a while. I broke this one in a bike crash in September 2015.

Weloop Tommy

Introduction to another smartwatch

I was reading daily news on my RSS feed and there is this article on HaD about an open source project OSSW by Krzysztof Szczesniak :

And I tought to myself this could be interesting. I am kind of interested in owning a watch that has an option/potential:

  • to be my silent alarm clock,
  • TOTP (“Timed One Time Password”)
  • lasts some 2 weeks of moderate use

I find mixed reviews about it, but trust that by contributing we can make it work, work better.
Read the rest of this entry »

Written by luftek

August 3rd, 2015 at 3:46 pm

Compact camera plastic gear repair, Canon A480

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I received a compact camera from the brother. He said he found it that way, broken or not working properly. With this he ment, lens mechanism was not extending and retracting as it should.

I had it stored for future repair time. Today I was again looking into it and found this page: http://chdk.wikia.com/wiki/A480 (CHDK РCanon Hack Development Kit). I thought to myself, I would like to use this. But first I wanted to see if anything can be done to repair mechanism.

I used YT disassembly movie as a reference. I opened and removed the parts in this order: back plastic, screen assembly and then lens with sensor assembly. Had to desolder 2 ribbon cables (one for photo interrupter, one prob. for focus). Then I could split assembly.

(1st pic) Lens assembly has a motor with worm gear on it and 3 reduction gears. White gear on the right (You can see clearly how plastic gears fit together. Last one in the chain is long black one (broken).
(2nd pic) Broken gear with missing axis part. This gear is long, because the lens assembly extends outward. Replacements are¬†sold on ebay for about 5‚ā¨¬†and ship¬†from far away, Hong Kong.
(3rd pic) 1,2 mm drill for making hole for replacement axis.
(4th pic) leg from diode rectifier used as axis.

Camera works now. Post with CHDK installed soon to come.

lens assembly broken gear, one side axis missing 1,25 mm drill axis transplant

Written by luftek

July 27th, 2014 at 8:05 pm

Posted in Repair

Worlde globe LED, night stand lamp

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I was thinking about adding light, to small world globe I have, for quite some time.
Yesterday I diffused 6 LEDs with sand paper and¬†soldered 6 of them (parallel) into a small blob. After drilling the holes in globe holder, I ran wires GND and +V through. Today I added a 2×56 ohm resistors (about 28 ohm, and 0.5W) for limiting resistor and a micro usb port.
When not charging my phone I can learn countries of the world (in German :))

Also nice present for a small kid, who likes to have lights when going to bed.

6 star LED illuminated globe europe, globe micro usb and limiting resistors

Written by luftek

July 27th, 2014 at 7:25 pm

Posted in Make

Hand watch – Ring of fire

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Well, I decided to remove the logo from a C**** World Time Illuminator watch I have and wear all the time now. I removed 4 screws from the back and made sure I didn’t lose the the gasket that keeps water or other liquids from entering.

There was not much in the housing. I pried out the plastic front end, reattached glass and already put everything together when decided to look for the led that illuminates the watch when pressed. It was orange led.

 before modification

Measurements showed it has a series resistor of 100 ohms and forward voltage of about 2V. Then I noticed 3 more SMD pads on other corners of the pcb. They were connected in parallel, which meant I could add 3 more LEDS for greater effect. ūüôā Found some small RED SMD 0805 LEDS and. Added 100 ohm in series for about 13mA per LED and after soldering with my 2nd soldering iron you can see the result. It’s like the ring of fire on my hand (in person).

testing in enclosure

Written by luftek

June 16th, 2014 at 9:02 pm

Posted in Repair